This invention is directed toward a method and an assemblage for controlling and managing the lower explosion level (LEL) in ovens or furnaces where a potentially explosive or combustible atmosphere can be created. The ovens or furnaces with which the method and assemblage of the invention can be used typically utilize ambient or heated air and are operated at about atmospheric or slightly negative pressure to process or dry products that contain potentially explosive or combustible volatile materials. For example, such ovens or furnaces are used to dry paints, powders, pharmaceutical formulations, and the like. They are also used in finishing processes which include dipped, coated, sprayed and impregnated materials or wood, paper and plastic pallets, spacers or packaging materials. In addition, these ovens and furnaces are employed in polymerization and resin curing processes. Potentially explosive or combustible materials that my be present in these processing and drying operations include quench oil, waterborne finishes, cooling oil, aromatics such as alcohols, organic solvents, and the like.
The National Fire Protection Agency (NFPA) has classified such ovens and furnaces as "Class A" and has established standards for their ventilation. These standards state that the LEL in Class A ovens and furnaces must not exceed 50% and the combustion level must be continuously monitored [See NFPA, Ovens and Furnaces, "NFPA 86 Standard for Ovens and Furnaces", 1985 Edition]. Many industrial insurers have adopted the NFPA standards for Class A ovens and furnaces in their policies.
Lower explosion level (LEL) is generally accepted to mean the lowest ratio of an explosive or combustible material to air at which the material will explode or combust. In other words, it is that concentration of an explosive or combustible material present in air at which the material will explode or combust.
In order to avoid a potentially dangerous explosive or combustible condition, many products containing volatile aromatics or solvents are dried on open trays or beds in large, enclosed areas at about ambient temperatures. These products are periodically, manually stirred in order to expose more of their surfaces as they are air-dried so that the volatile aromatices or solvents contained in them can slowly evaporate into the air. This type of open bed or tray drying is cumbersome, time consuming and labor intensive. By employing the method and assemblage of this invention, these products can now be safely, quickly and economically dried in Class A ovens or furnaces.